A fleece layer of the previously described type is known from EP 0 865 521 B1, in which a first card web conveyor belt supplying the card web is routed both through the upper carriage and through the laying carriage and then continues through an auxiliary carriage, which can be moved back and forth underneath and transversely to the output conveyor belt. This auxiliary carriage supports a tensioning roll and serves to keep the card web conveyor belt under tension. A second card web conveyor belt is also routed through the upper carriage and the laying carriage and then passes through a second auxiliary carriage, which can be moved back and forth underneath and transversely to the output conveyor belt in the machine stand; this auxiliary carriage supports another tensioning roll and serves to keep the second card web conveyor belt under tension.
In the upper carriage, the first card web-supplying conveyor belt travels over two rollers, which are arranged at different heights and which are offset from each other transversely to their axial direction, so that the web entrance slants downward. This slanted web entrance in the upper carriage is accompanied by the second web card conveyor belt, which proceeds from there to the area between the upper carriage and the laying carriage, where it extends parallel to the first web conveyor belt, together with which it encloses, sandwich-like, the card web to be laid. The two web conveyor belts cannot be routed so that they are parallel to each other at the lower deflecting roll in the upper carriage because different wrap-around radii are present, which would lead to frictional effects potentially damaging to the guided card web. The second web conveyor belt is therefore routed through the upper carriage over a total of four separate deflecting rollers in the area of the previously mentioned lower deflecting roller before it approaches the first web conveyor belt again. Corresponding measures are also taken for the first web conveyor belt in the laying carriage, because this belt, for the same reasons as those explained above, cannot be guided together with the second web conveyor belt into the laying gap in the laying carriage.
The strands of the two web conveyor belts leaving the laying carriage at the laying gap extend just above the output conveyor belt and take over there the function of covering the laid fleece to protect it from aerodynamic disturbances caused by the movement of the laying carriage.
What is obtained overall, therefore, is a very complicated routing of the two web conveyor belts both in the upper carriage and in the laying carriage and also in the two tension carriages. There are thus a large number of belt deflection points, and the belts are of considerable length.
A much simpler and shorter routing of the belts participating in the transport of the card web is present in the carriage cross-lappers described in Vliesstoffe (Nonwovens) by W. Albrecht, H. Fuchs, and W. Kittelmann (published by Wiley-VCH, Weinheim, 2000, p. 161). The advantage of this type of fleece layer is to be found in the extremely simple way in which the belts participating in the transport of the card web are routed, all of the belts being relatively short and traveling over only a few deflection points. Nevertheless, the route taken by the card web through the layer is open, and so is the deposition of the web on the output conveyor belt. As a result, the card web is exposed to strong aerodynamic influences, which are caused by the movement of the carriages and which can have the effect of blowing the fibers away and of causing the web to be deposited nonuniformly, especially at the edges of the laid nonwoven. The working speed of a fleece layer of this type is therefore very limited. Another disadvantage of the carriage cross-lappers mentioned above is that they cannot exert any pressure on the top side of the laid fleece without causing significant distortions, pile-ups, and folds in the fleece. This type of layer has therefore been displaced by double-belt layers, for which the fleece layer according to the previously mentioned EP 0 865 521 B1 can serve as one of many examples. In this type of layer, the card web, as it travels though the machine, is guided horizontally between two belts, one on each side, which explains why this is also called a “sandwich layer”. In the layers of the type just described, these belts also serve as a covering for the nonwoven which has been deposited on the output conveyor belt and thus protect it from the previously mentioned air turbulence, although at the cost of the previously described complicated belt routing.